Rhizosphere microbial communities explain positive effects of diverse crop rotations on maize and soybean performance

Microorganisms play essential roles in agricultural systems, and their abundance, diversity and activity can be influenced by management practices. Crop rotational diversity is known to influence both soil microorganisms and crop productivity, yet the specific contributions of microorganisms to rotational benefits are unknown. To facilitate monitoring soil biological processes that support vigorous and high yielding crops, we studied maize (Zea mays L.) and soybean (Glycine max L.), and their associated microorganisms within a two-year maize-soybean rotation and within four-year crop rotations with varying crop sequences. We hypothesized that rhizosphere microbial communities are strong predictors of crop productivity contingent on rotational diversity and previous crop legacy. Sampling at seedling and flowering stages, we assessed rhizosphere bacterial and fungal communities, soil and plant tissue nutrients, aboveground biomass, and yield. Rhizosphere communities varied with rotational diversity and previous crop legacy. Concurrently, maize and soybean yield and biomass were approximately 15–25% larger in more diverse rotations and with different crop legacies, but there were no crop rotational effects on tissue or soil nutrients. Yield differences across rotational diversity or previous crop legacy were better predicted when microbial communities were considered. Fungal communities predicted lower maize seedlings biomass when following soybean, and lower soybean seedling biomass when following maize, independent of rotational diversity. Further, for maize, fungal communities predicted lower maize yield in the maize-soybean rotation, while in the four-year diverse rotations, bacterial communities predicted maize recovery from a soybean legacy by flowering. These results suggest that benefits of four-year rotations in maize and soybean production are driven by changes in plant pathogenic communities.